The present invention relates to a common salt having the rounded-off savory taste of natural common salt and a reduced tendency toward deliquescence and coagulation. More particularly, the present invention relates to a common salt which has an improved mouth-feel realized by inclusion of the mineral fraction of seawater and is free from the objectionable tendency toward deliquescence and coagulation. The present invention further relates to a method of producing said common salt and a production apparatus for reducing the method to practice.
Furthermore, the present invention relates to a method for effective utilization of seawater in the production of said common salt. More particularly, the invention relates to a process for fractitonally recovering a raw material or materials for said common salt from the freshwater fraction of seawater and producing said common salt from said raw material or materials.
The unrefined common salt available from seawater contains seawater minerals (bittern), inclusive of magnesium chloride, and has a pleasing salty taste which cannot be obtained with refined common salt. However, since bittern has the property to absorb moisture from the atmosphere and undergoes deliquescence, the unrefined common salt is hygroscopic due to the deliquescent property of the bittern and undergoes coagulation with time (coagulability) with the consequent disadvantage of a short shelf-life and difficulties in handling.
To overcome the above disadvantages, a common salt highly purified by removing bittern by an ion exchange technique and containing NaCl in a high concentration (not less than 99.4%) has heretofore been used as the table common salt. As produced by the above procedure, the table common salt has no deliquescent property and is easy to handle but has the shortcoming that it lacks the inherent savory salty taste of the bittern.
Under the circumstances, a variety of processed salts overcoming the hygroscopicity and other drawbacks of common salt have been proposed. JP 55(1980)-16625, B for instance, discloses a processed salt with said hygroscopicity reduced by depositing a sodium or potassium salt of organic acid on the surface of common salt crystals. JP 54(1979)-25105, B discloses a processed salt prepared by coating common salt crystals with a minor amount of a stevia extract to thereby augment the characteristic pleasing taste and reduce the hygroscopicity of common salt. Furthermore, JP 1(1989)-181762, A discloses a processed salt comprising a core comprised of a seasoning or flavor material hermetically enshrouded with a crystalline salt coating. In the processed salt disclosed in JP Kokai H1-181762, the salty taste has been supplemented with a savory taste derived from the seasoning material used as the core.
The present invention has for its object to overcome the drawbacks of the prior art relating to common salt and thereby provide a common salt which is tasteful and easy to handle and a method for its production.
More particularly, the first object of the present invention is to provide a common salt which has the savory, salty taste characteristic of natural salt retained through inclusion of the mineral component of seawater and reduced in the tendency toward deliquescence and coagulation, hence having been improved in storage stability and ease of handling. The second object of the invention is to provide a method of producing said common salt and an apparatus suitable for practicing said method.
Thirdly, it is also an object of the invention to implement an effective utilization of seawater in the production of common salt by recovering a raw material for said common salt from seawater efficiently and without involving a waste of the seawater and insure an effective utilization of the byproduct freshwater. Stated differently, the invention further provides a method for effective utilization of seawater.
The inventors of the present invention made an intensive research with an aim at improving the taste and inhibit deliquescence of common salt and found that when a bittern-containing composition rich in bittern is used as a core and the surface of this core is covered with sodium chloride or a sodium chloride-containing composition optionally containing calcium sulfate or bittern, the proportion of said bittern being smaller than that of the core composition, not only the tendency toward deliquescence can be significantly inhibited but a common salt having a savory taste characteristic of natural salt can be produced.
The present invention has been developed on the basis of the above finding.
The present invention, therefore, is directed to the common salts defined in the following paragraphs (1)xcx9c(4).
(1) A bittern-containing granular common salt characterized in that each grain thereof comprises a core comprised of a bittern-containing composition optionally containing sodium chloride and, as covering the surface of said core, a coating layer comprised of a sodium chloride-containing composition optionally containing calcium sulfate.
(2) A bittern-containing granular common salt as defined in (1) above further characterized in that the coating layer is comprised of a composition containing bittern and sodium chloride and that the proportion of bittern formulated in said coating layer is smaller than the proportion of bittern formulated in the bittern-containing composition of which the core is comprised.
(3) A bittern-containing granular common salt as defined in (1) or (2) further characterized in that the proportion of bittern formulated in the bittern-containing composition of which the core is comprised is 15xcx9c90 weight % per 100 weight % of the core.
(4) A bittern-containing granular common salt as defined in (2) or (3) further characterized in that the proportion of bittern formulated in the coating layer is not more than 10 weight %, preferably not more than 5 weight %, per 100 weight parts of the coating layer.
The present invention is further directed to the following methods (5)xcx9c(8) for producing said common salts:
(5) A method of producing the bittern-containing granular common salt defined in (1) which comprises spraying the surface of said core grain comprised of a bittern-containing composition optionally containing sodium chloride with an aqueous solution of sodium chloride optionally containing calcium sulfate and drying the same to coat said core grain with a sodium chloride-containing composition optionally containing calcium sulfate.
(6) A method of producing the bittern-containing granular common salt defined in (3) or (4) which comprises spraying the surface of said core comprised of a bittern-containing composition optionally containing sodium chlorlde with an aqueous solution of sodium chloride containing a smaller proportion of bittern than the bittern content of said core grain and drying the same to coat said core grain with a composition containing both bittern and sodium chloride.
(7) A method of producing the bittern-containing granular common salt defined in (1) which comprises feeding core grains comprised of a bittern-containing composition optionally containing sodium chloride and coating grains comprised of a sodium chloride-containing composition optionally containing calcium sulfate to a spray dryer and spraying those grains with a binder to cause said coating grains to be deposited on the surface of each of said core grains to form a coating layer.
(8) A method of producing the bittern-containing granular common salt defined in any of (2) through (4) which comprises feeding core grains comprised of a bittern-containing composition optionally containing sodium chloride and coating grains comprised of a composition containing sodium chloride and bittern, the proportion of the bittern being smaller than the bittern content of said core grains to a spray dryer and spraying those grains with a binder to cause the coating grains to be deposited on the surface of each core grain to form a coating layer.
The present invention is further directed to apparatuses (9)xcx9c(11) for production of the above common salts.
(9) A spray dryer comprising a casing equipped with an air supply port, an exhaust port and a discharge port for withdrawing product bittern-containing common salt grains, a feeder for feeding core grains comprised of a bittern-containing composition optionally containing sodium chloride into said casing, a nozzle for spraying an aqueous sodium chloride solution optionally containing calcium sulfate or bittern against the feed core grains, a spray solution supplier for feeding said aqueous sodium chloride solution to said nozzle, an air feeder for supplying drying air into the casing, and a discharger for discharging the product bittern-containing common salt grains into the outside of the casing.
(10) A spray dryer characterized by its comprising a casing equipped with an air supply port, an exhaust port and a discharge port for withdrawing product bittern-containing common salt grains, a feeder for feeding core grains comprised of a bittern-containing composition optionally containing sodium chloride and coating grains comprised of a sodium-chloride containing composition optionally containing calcium sulfate or bittern into the casing, a nozzle for spraying a binder against the feed core grains and coating grains, a spray solution supplier for feeding said binder to said nozzle, an air feeder for supplying drying air into the casing, and a discharger for discharging the product bittern-containing common salt grains into the outside of the casing.
(11) A spray dryer comprising a casing equipped with an air supply port, an exhaust port and a discharge port for withdrawing product bittern-containing common salt grains, a nozzle for spraying an aqueous solution of a bittern-containing composition optionally containing sodium chloride into said casing, a spray solution supplier for feeding said aqueous bittern-containing composition solution to said nozzle, a nozzle for spraying an aqueous sodium chloride-containing solution optionally containing calcium sulfate or bittern into said casing, a spray solution supplier for feeding said aqueous sodium chloride-containing solution to the nozzle mentioned just above, an air feeder for supplying drying air into the casing, and a discharger for discharging the product bittern-containing common salt grains.
The present invention is further directed to the following methods (12) and (13) for separating and recovering freshwater, a sodium chloride-containing composition and a bittern-containing composition efficiently from seawater.
(12) A method for fractional recovery of freshwater, a sodium chloride-containing composition and a bittern-containing composition from seawater comprising either a step of subjecting seawater to a reverse osmosis membrane treatment to fractionate it into freshwater and a salt-containing water and subjecting the salt-containing water to an ion exchange treatment to fractionate it into a sodium chloride-containing composition and a bittern-containing composition or a step of subjecting seawater to an ion exchange treatment to fractionate it into an aqueous sodium chloride-containing solution and an aqueous bittern-containing solution, and subjecting the aqueous sodium chloride-containing solution and aqueous bittern-containing solution respectively to a reverse osmosis membrane treatment to fractionate it into freshwater and a sodium chloride-containing composition or a bittern-containing composition.
(13) A method for fractional recovery of freshwater, a sodium chloride-containing composition and a bittern-containing composition from seawater comprising a step of subjecting seawater to a reverse osmosis membrane treatment to fractionate it into freshwater and a salt-containing water, a step of subjecting the salt-containing water obtained in the above step to an ion exchange treatment to fractionate it into a sodium chloride-containing composition and a bittern-containing composition, and a step of subjecting the sodium chloride-containing composition or bittern-containing composition obtained in the above step further to a reverse osmosis membrane treatment to fractionate it into freshwater and either a sodium chloride-containing composition or a bittern-containing composition.
Stated differently, the above methods for fractional recovery is a method for producing freshwater, a sodium chlorlde-containing composition and a bittern-containing composition using seawater as the raw material. Therefore, the present invention encompasses the freshwater, sodium chloride-containing composition and bittern-containing composition obtainable by the above production method.
The present invention is further directed to the following common salt produced from said seawater-derived sodium chloride-containing composition and bittern-containing composition and to the following method of producing the common salt.
(14) A bittern-containing granular common salt as defined in any of the above paragraphs (1)xcx9c(4) as prepared by using the sodium chlorlde-containing composition and bittern-containing composition obtainable by the above method (12) or (13) as the sodium chloride-containing composition optionally containing calcium sulfate or bittern, and the bittern-containing composition optionally containing sodium chloride, respectively.
(15) A method of producing a bittern-containing granular common salt as defined in any of the above paragraphs (5) through (8) characterized in that bittern-containing common salt grains are produced by a spray drying technique using the sodium chloride-containing composition and bittern-containing composition obtainable by the above method (12) or (13) as the sodium chloride-containing composition optionally containing calcium sulfate or bittern and the bittern-containing composition optionally containing sodium chloride, respectively.